Toroidal type deflection coils for cathode ray tubes

ABSTRACT

In a toroidal type deflection coil for use in a cathode ray tube of the type comprising a funnel shaped magnetic core and a coil wound about the core to create a magnetic field having different distributions at the fore and rear edges of the core, portions of the peripheries of the fore and rear edges of the core on which the coil is wound take the form of curves of different radii of curvature.

United States Patent Sawada [54] TOROIDAL TYPE DEFLECTION COILS FOR CATHODE RAY TUBES Elli Sawada, Tokyo, Japan Denki Onkyo Company Limited, Tokyo, Japan Filed: Jan. 28, 1971 Appl. No.: 110,724

inventor:

Assignee:

Foreign Application Priority Data Jan. 30, 1970 Japan ..45/8193 US. Cl ..335/210, 313/76 Int. Cl ..H0lf 7/00 Field of Search ..335/210, 213, 297; 313/75,

[ Sept. 26, 1972 [56] References Cited UNITED STATES PATENTS 3,081,420 3/1963 Marley ..335/213 3,246,192 4/1966 Torsch ..335/213 X Primary Examiner-George Harris AttorneyChittick, Pfund, Birch, Samuels & Gauthier 5 7 ABSTRACT In a toroidal type deflection coil for use in a cathode ray tube of the type comprising a funnel shaped magnetic core and a coil wound about the core to create a magnetic field having different distributions at the fore and rear edges of the core, portions of the peripheries of the fore and rear edges of the core on which the coil is wound take the form of curves of different radii of curvature.

2 Claims, 5 Drawing Figures PKTENiEDSEPZs me I v 3.694.781

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' PRIOR ART PR/OR ART INVENTOR EIJI SAWADA SM 5 G ATTORNEY BACKGROUND O THE, INVENTION This invention relates to a toroidal deflection coil for cathode ray tubes.

In a television receiver, it is necessary to use a deflection yoke or coil capable of producing a distribution of a deflection field suitable for a particular cathode ray tube by considering the configuration of the tube or the space through which a electron beam passes. Thus for example, a deflection yoke capable of producing a uniform field distribution is suitable for a narrow deflection angle cathode ray tube whereas a deflection the tube.

Deflection coils are classified into two types, that is thesaddle type wherein the deflection coil is comprised by two spaced apart coil sides extending substantially in parallel with the tube axis and two arcuate coil sides interconnecting the ends of the first mentioned coil sides and extending circumferentially of the tube neck, and

toroidal type wherein the coil conductor is wound helically about a toroidal core concentric with the tube neck. These two types of deflection coils have inherent advantages and disadvantages but by taking into consideration their efficiency and economy, the saddle type defection coils are generally used as the horizontal deflection coils and the toroidal type deflection coil are used as the vertical deflection coils of television receiving tubes.

In a multiple electron beam color receiving tube of the class wherein trios of small phosphor dots are regularly arranged on the screen of the receiving tube and a plurality of electron beams focused on the same point is deflected to scan the screen for exciting the luminescing respective dots of the phosphors the distribution of the deflection magnetic field should be of the so-called bobbin type distorted field in order to minimize the focusing error.

It is very easy to manufacture a saddle type deflection coil capable of creating such a bobbin type distorted deflection coil but not to manufacture a toroidal type deflection coil that can create the same distribution.

More particularly, as shown in FIGS. 1 and 2, in the prior art in a saddle type deflection coil generally designated by S it is easy to vary the distribution of the field to have any shape varying between a barrel type and a bobbin type by varying the distribution of coil conductors included in an angle 0 with reference to the axis 0 of the tube.

Since the saddle type deflection coil is manufactured by inserting the conductors in grooves in a metal form which are distributed to create the desired field distribution, such adjustment of the field distribution can be readily made by the suitable design of the pattern of the grooves without the necessity of changing the method of winding. The bobbin type distorted deflection field can be readily created by varying in the longitudinal direction the width of gap W, generally termed a window, defined between conductor groups On the other hand, since the toroidal type deflection coil is fabricated by the steps of supporting the toroidal core by a rotary arbor extending through the core and helically winding the conductor about the core by rotating the rotary arbor it isimpossible to vary the distribution or density of the conductor along any arcurate segment on a circle about the tube axis.

Thus, as shown in FIG. 3, when a conductor 2 is wound spirally about a funnel shaped core 1 having a larger fore end diameter d, than the rear end diameter d, the conductor 2 forms portions of the outer surface of a frustum of a cone between the fore and aft edges 11 and 12 so that the distribution of the conductor in planes perpendicular to the axis 0 x are similar.

For this reason, by the prior method of winding the toroidal deflection coil, it has been impossible to vary the deflection field along the axis between the fore and aft edges of the yoke so that it has been impossible to obtain a deflection coil capable of creating a desired magnetic field distorted not only as a whole but also at the fore and aft edges along the tube axis which is required by a color television receiving tube utilizing a plurality of electron beams.

For this reason, in the prior art toroidal deflection coil, where it is necessary to increase the density of the conductor 2 at the rear edge 12 more than at the fore edge 11 as diagrarmnatically shown in FIG. 4,the axis 0 of the toroidal core 1 is shifted laterally so as to wrap the left and right hand conductor groups S, and S by rotating the core respectively about different centers 0 and 0 Such a method of winding the coil requires a complicated coil winding apparatus.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel toroidal deflection coil capable of creating different magnetic field distributions at the fore and rear edges of the core and yet can be manufactured by a prior coil winding machine of simple construction.

A more specific object of this invention is to provide an improved toroidal type deflection coil suitable for use in a color television receiving tube capable of creating desirable field distributions with a minimum focusing error.

According to the invention, in a toroidal type deflection coil for use in a cathode ray tube, particularly a color television cathode ray tube utilizing a plurality of electron beams of the type comprising a funnel shaped magnetic core and a coil wound about the core to create a magnetic field having different distribution at the fore edge and the rear edge of the core, portions of the peripheries of the fore and rear edges of the core on which the coil is wound take the form of curves of different radii of curvature.

The above described portion of the fore edge is in the form of an ellipse or an oblong circle whereas those of the rear edge is in the form of a circle.

BRIEF DESCRIPTION OF THE DRAWING The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing in which FIG. 1 is a perspective view of a saddle type deflection coil,

FIG. 2 is a diagrammatic end view of a prior saddle type deflection coil showing the distribution of the coil conductor;

FIG. 3 shows a longitudinal section of a prior art toroidal type toroidal deflection coil;

FIG. 4 shows an end view of one half of the toroidal type deflection coil shown in FIG. 3 and is useful to explain a prior method of winding the deflection coil and FIG. 5 shows an end view, partly in transverse section of a toroidal deflection coil embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As diagrammatically shown in FIG. 5, according to this invention, the inner and outer peripheries of the fore edge 11 and the rear edge 12 of a cylindrical core 1 of magnetic material, ferrite for example, on which the coil is to be wound are formed by curves of different radii of curvature. For example, the fore edge takes the form of an oblong circle or an ellipse whereas the rear edge 12 a circle.

When a conductor is wound about the cylindrical core having such a special configuration by a conventional toroidal coil winding machine by rotating the core about its center 0 the density of the conductor becomes higher at the rear edge than at the fore edge so as to increase the intensity of the bobbin shaped distorted magnetic field at the rear edge of the core. Such a distorted distribution of the field is particularly suitable for a color television receiving tube utilizing a plurality of electron beams.

Thus, this invention provides a novel toroidal type deflection coil for color cathode ray tubes capable of producing different field distributions at the front and rear edges of the coil and can be readily wound with a simple prior art toroidal coil winding machine. Further, it is possible to vary in any desired manner the field distribution along the longitudinal axis of the coil by continuously varying the cross sectional configuration of the coil along the longitudinal axis thereof from the fore edge to the rear edge, thus providing a novel toroidal deflection coil manifesting an ideal field distribution having lesser focusing error than the deflection coil of the prior design requiring complicated method and apparatus for winding.

Although the invention has been shown and described in terms of a preferred embodiment it should be understood that the invention is by no means limited to this particular embodiment but can be modified in various manners without departing from the true spirit and scope of the invention as defined in the appended claims.

fy pe deflection coil for use in a cathode ray tube utilizing a plurality of electron beams of the type comprising a funnel shaped magnetic core and a coil wound about said core to create a magnetic field having different distributions at the fore edge and the rear edge of said core characterized in that portions of the inner and outer peripheries of said fore edge of said core on which said coil is wound take the form of curves of different curvature than portions of the inner and outer peripheries of said rear edge of said core on which said coil is wound.

2. The toroidal type deflection coil as defined in claim 1 wherein the configuration of said portions of said fore edge are in the form of an oblong circle or an ellipse and that of the portions of said rear edge are in the form of a circle. 

1. A toroidal type deflection coil for use in a cathode ray tube utilizing a plurality of electron beams of the type comprising a funnel shaped magnetic core and a coil wound about said core to create a magnetic field having different distributions at the fore edge and the rear edge of said core characterized in that portions of the inner and outer peripheries of said fore edge of said core on which said coil is wound take the form of curves of different curvature than portions of the inner and outer peripheries of said rear edge of said core on which said coil is wound.
 2. The toroidal type deflection coil as defined in claim 1 wherein the configuration of said portions of said fore edge are in the form of an oblong circle or an ellipse and that of the portions of said rear edge are in the form of a circle. 